Coupling with a palladium salt

ABSTRACT

A PROCESS IS PROVIDED FOR THE COUPLING OF AROMATIC COMPOUNDS TO PRODUCE POLYNUCLEAR AROMATIC COMPOUNDS WHEREIN THE REACTION IS CARRIED OUT IN LIQUID HYDROGEN FLUORIDE WITH A PALLADIUM SALT AS THE SOLE COUPLING AGENT. THE PROCESS IS OF PARTICULAR IMPORTANCE IN THE COUPLING OF ELECTRONEGATIVELY SUBSTITUTED AROMATIC COMPOUNDS WHEREBY THE MAJOR COUPLING TAKES PLACE IN THE POSITION ORTHO TO THE ELECTRONEGATIVE GROUP.

United States Patent 3,748,350 COUPLING WITH A PALLADIUM SALT Roy R. Josephson, West Marlborough Township, Chester County, Pa., assignor to Hercules Incorporated, Wilmington, Del. No Drawing. Filed Dec. 29, 1969, Ser. No. 888,904 Int. Cl. C07c /12, 15/14 US. Cl. 260-475 R 7 Claims ABSTRACT OF THE DISCLOSURE A process is provided for the coupling of aromatic compounds to produce polynuclear aromatic compounds wherein the reaction is carried out in liquid hydrogen fluoride with a palladium salt as the sole coupling agent. The process is of particular importance in the coupling of electronegatively substituted aromatic compounds whereby the major coupling takes place in the position ortho to the electronegative group.

This invention relates to a process of coupling aromatic compounds toproduce polynuclear aromatic compounds and more particularly to a process of coupling aromatic compounds containing electronegative groups whereby the coupling is primarily ortho to said groups.

It is well known that aryl compounds can be coupled by means of palladium salts but when the process is applied to aromatic compounds containing electronegative groups, the major coupling takes place in the meta or para position. It has previously been possible to couple such aryl compounds in the ortho position only by processes involving several steps, including the preparation of an intermediate compound having a metallo group in the position ortho to the electrouegative group.

Now in accordance with this invention it has been found that aryl compounds containing electronegative groups such as nitro, carboxy, and carboalkoxy, can be coupled in the ortho position in a simple one-step operation by using a palladium salt as the coupling agent and carrying out the reaction in liquid hydrogen fluoride.

While the process of this invention can be applied to the coupling of a wide variety of aromatic compounds which have a labile hydrogen atom, it is surprising and unique when applied to an electronegatively substituted aryl compound in producing an ortho coupling reaction in place of the normal para coupling reaction. Thus aromatic compounds, i.e., a benzene, naphthalene, anthracene, etc., compound, containing a nitro, carboxy, or carboalkoxy group can be coupled in the ortho position.

Any aromatic compound having the formula where Ar is any aromatic nucleus such as that of henzene, naphthalene, biphenyl, anthracene, etc., X is H or an alkyl of 1 to 3 carbon atoms, halogen, nitro, carboxy or carboalkoxy, where the alkoxy group contains 1 to 3 carbon atoms, and R is H or an alkyl of 1 to 3 carbon atoms or can be halogen when X is halogen can be coupled by the process of this invention. Exemplary of these aromatic compounds are aromatic hydrocarbons such as benzene, naphthalene, biphenyl, anthracene, etc., and their monoand dialkyl-substituted derivatives such as toluene, o-, m-, and p-xylene, ethylbenzene, cumene, cymene, etc., nitro-substituted aryls such as nitrobenzene, o-nitrotoluene, p-nitrotoluene, etc., carboxy-substituted aryls such as benzoic acid, 0-, mand p-toluic acid, naphthoic acid, etc., halogen-substituted aryls such as chloro-, bromo-, fluoroand iodo-benzene, 1,2-dichlorobenzene, 1,4-dichlorobenzene, o-, mand p-chlorotoluene, etc., and carboalkoxy-substituted aryls such as methyl,

3,748,350 Patented July 24, 1973 ethyl, propyl, and isopropyl benzoate, and the corresponding esters of the toluic acids, naphthoic acid, etc.

The process of this invention can be carried out at any convenient temperature but generally will be carried out within the range of from about 20 to about 150 C. The preferred temperature will depend on the reactivity of the aromatic compound being coupled, the more reactive ones being run at the lower temperatures and the less reactive ones at the higher temperatures. In some cases the temperature to be used will depend upon the desired isomer that will be produced. Suflicient pressure will be applied at the prevailing temperature to maintain the hydrogen fluoride in the liquid phase. Thus, the pressure will range from slightly above atmospheric at 20 C. to about p.s.i.g. at a reaction temperature of C.

Any palladium salt that has substantial solubility in the liquid hydrogen fluoride reaction medium or that is converted to a fluoride or to a complex in the hydrogen fluoride, can be used as the coupling agent in the process of this invention. Exemplary of the palladium salts, or compounds that are converted to such in situ, are the palladium salts of alkanoic acids having 2 to 10 carbon atoms such as palladium acetate, propionate, butyrate, octanoate, decanoate, etc., palladium fluoride, palladium nitrate, palladium oxide, palladium metal, palladium acetylacetonate, etc. While a stoichiometric amount of the palladous salt is required for the coupling reaction, i.e., 1 mole per 2 moles of the aromatic compound being coupled, the palladium metal that is formed can be reoxidized. Hence the amount of palladous salt can be varied over a wide range, but generally will be within the range of from about 0.5 mole per mole of aromatic compound to about 1 mole per 10 moles of aromatic compound.

The process is generally carried out under substantially anhydrous conditions. However, if palladous oxide is used, there will, of course, be water formed during the reaction. In any event, anhydrous conditions are not essential and water in amounts up to about 20% or more of the hydrogen fluoride diluent can be tolerated without adversely affecting the reaction, although at the higher amounts the reaction rate is reduced.

The following examples will illustrate the process of this invention. All parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 A polyethylene reaction vessel equipped with a magnetic stirrer was charged with 1.0 g. of palladium acetate and 10 ml. of liquid hydrogen fluoride. To the stirred solution held at 10 C. was added 5 ml. of benzene. The reaction mixture was allowed to warm to 18 C. and was stirred for 1 hour. The hydrogen fluoride was then removed by evaporation under a stream of nitrogen at room temperature. Five ml. of hexane was then added and the solution on analysis by gas-liquid chromatography was found to contain 1.8% w./v. of biphenyl.

EXAMPLE 2 The procedure of Example 1 was repeated except that 5 ml. of toluene was substituted for the benzene used in that example. Gas-liquid chromatography showed the hexane solution to contain 1.6% w./v. of p,p'-bitoly1.

EXAMPLE 3 The procedure of Example 1 was repeated except that 5 ml. of o-xylene was substituted for the benzene used in that example. Gas-liquid chromatography showed the hexane solution to contain 3.3% w./v. of 3,4,3',4'-tetramethylbiphenyl and 0.3% w./v. of another isomer of tetramethylbiphenyl.

3 EXAMPLE 4 The procedure of Example 1 was repeated except that 2.0 ml. of nitrobenzene was substituted for the benzene used in that example and the reaction mixture was stirred at room temperature for 2 weeks. After removing the hydrogen fluoride, there was added to the reaction mixture 100 ml. of acetone. Analysis of the acetone solution by gas-liquid chromatography showed it to contain 0.86% w./v. of 2,2-dinitrobiphenyl, which is 78% of the theoretical yield. A small amount of solid calcium chloride was added to the acetone solution to neutralize any remaining hydrogen fluoride and to absorb any water. The mixture was filtered, the acetone evaporated and the product recrystallized to yield the 2,2'-dinitrobiphenyl having a melting point of 122-124 C.

EXAMPLE 5 The procedure of Example 4 was repeated except that methyl benzoate was used in place of nitrobenzene and at the end of the reaction period, after removal of the hydrogen fluoride, 100 ml. of methanol was added in place of acetone. Analysis of the methanol solution by'gasliquid chromatography showed it to contain 0.93% w./v. of 2,2'-dicarbomethoxy biphenyl (the dimethyl ester of diphenic acid), which is 75% of the theoretical yield.

EXAMPLE 6 A mixture of 1.0 g. of palladium acetate, 2.0 g. of benzoic acid and ml. of liquid hydrogen fluoride, in a polyethylene reaction vessel equipped with a magnetic stirrer, was stirred at room temperature for 4 days. The hydrogen fluoride was removed by evaporation and 20 ml. of pyridine was added, followed by 1.0 ml. of N,O-bis(trimethylsilyl)acetamide. Analysis by gas-liquid chromatography showed the pyridine solution to contain the bis(trimethylsilyl) ester of diphenic acid.

EXAMPLE 7 A mixture of 1 ml. of nitrobenzene, 5.0 ml. of liquid hydrogen fluoride and 1.0 millimole of palladium acetylacetonate, in a Teflon-lined reaction vessel equipped with a magnetic stirrer was stirred for 4 hours at 50 C. After removal of the hydrogen fluoride, 10 ml. of acetone was added. Analysis by gas-liquid chromatography showed the acetone solution to contain 1.5% w./v. of 2,2'-dinitrobiphenyl, i.e., a 68% conversion based on palladium.

EXAMPLE 8 Example 7 was repeated except that 1 ml. of methyl benzoate was substituted for the nitrobenzene used in that example and after removal of the hydrogen fluoride, 10 m1. of methanol was added in place of acetone. Analysis of the methanol solution by gas-liquid chromatography showed it to contain 1.4% w./v. of 2,2'-dicarbomethoxybiphenyl, i.e., a 58% conversion based on palladium.

EXAMPLE 9 The procedure of Example 1 was repeated except that 2.0 g. of biphenyl was substituted for the benzene used in that example and the residue after removal of the hydrogen fluoride was treated with 5 ml. of hot acetic acid. The hot acetic acid was shown to contain quaterphenyl by gas-liquid chromatography.

EXAMPLE 10 The procedure of Example 1 was repeated except that 2.0 g. of naphthalene was substituted for the benzene and 4 millimoles of palladium fluoride was used in place of the palladium acetate used in that example. After removal of the hydrogen fluoride the residue was treated with hot ethanol. Binaphthyl was found in the hot ethanol by gasliquid chromatography.

4 EXAMPLE 11 A polyolefin reaction vessel equipped with a magnetic stirrer was charged with 0.03 mole of palladium acetate, 0.12 mole of chlorobenzene and 20 ml. of hydrogen fluoride. The mixture was stirred at room temperature for 6 hours. The hydrogen fluoride was removed by evaporation and the residue was extracted with hot benzene. Distillation of the benzene solution yielded 2.9 g. of the mixed isomers of dichlorobiphenyl having a boiling point range of -200 C. at 3 mm. pressure. This was a 43.3% conversion based on palladium.

The process of this invention makes it possible to produce diaryl compounds having wide utility. For example, the dinitro-diaryls can be reduced to the corresponding diaminodiaryls useful in the preparation of polyamides and polyimides. The tetraalkyldiaryls can be oxidized to tetracarboxylic acids and their anhydrides, useful for the preparation of polyimides and the dicarboxylic-diaryls are useful for the preparation of polyesters, polyamides, and polyimidazoles. Many other uses for the polyfunctional diaryls produced will be obvious to those skilled in the art.

What I claim and desire to protect by Letters Patent is:

1. The process for producing a diaryl compound by a coupling reaction, which process comprises contacting an aromatic compound having the formula RArX where Ar is an aromatic nucleus, X is H, an alkyl of 1 to 3 carbon atoms, halogen, nitro, carboxy, or carboalkoxy and R is H or an a'lkyl of 1 to 3 carbon atoms or halogen when X is halogen, with, as the sole coupling agent, a palladium salt in liquid hydrogen fluoride, the amount of said palladium salt being from about 0.1 to about 0.5 mole per mole of said aromatic compound being coupled.

2. The process of claim 1 wherein the palladium salt is a palladous salt of an alkanoic acid containing 2 to 10 carbon atoms.

3. The process of claim 2 wherein the palladous salt is palladium acetate.

4. The process of claim 1 for producing 2,2'-dinitrobiphenyl which comprises contacting nitrobenzene with palladium acetate.

5. The process of claim 1 for producing 2,2'-dicarbomethoxybiphenyl which comprises contacting methyl benzoate with palladium acetate.

6. The process of claim 1 for producing diphenic acid which comprises contacting benzoic acid with palladium acetate.

7. The process of claim 1 for producing tetramethyldiphenyl which comprises contacting o-xylene with palladium acetate.

References Cited UNITED STATES PATENTS 3,401,207 9/1968 Selwitz 260670 3,481,997 12/1969 Vanderwerlf 260670 3,145,237 8/1964 Van Helden 260'--649 3,316,290 4/1967 Fenton 260-484 3,413,352 11/1968 Heck 260--515 P 3,539,622 11/1970 Heck 260515 P 3,547,790 12/1970 Dannels et a1 260649 D OTHER REFERENCES Dannels et al., Reductive Coupling-CA, vol. 71 (1969).

Ichikawa et al., Oxidative Coupling-CA 70 (1969).

LORRAINE A. WEINBERGER, Primary Examiner R. D. KELLY, Assistant Examiner U.S. Cl. X.R.

260515, P, 645, 649 R, 649 D, 670 

